The invention relates to a digital data distributing technique in a satellite digital broadcast, communication of multimedia content, or the like and, more particularly, to a technique for distributing digital data constructed by commands of a computer language.
In more detail, the invention relates to a digital data distributing technique for distributing digital data in a markup language (for example, XML (eXtensible Markup Language)) format using a tag which can be arbitrarily defined and, more particularly, to digital data distribution for improving a transmitting efficiency of distribution content comprising text data such as what is called a script or the like and an executing efficiency on the reception side.
In a technical field of a broadcast, digitization of data is rapidly being promoted. A digital signal has a more excellent stability and a higher data compression ratio than those of an analog signal. According to the digital signal, a larger number of channels than that of the analog signal can be assured in a predetermined band irrespective of a cable, a ground wave, and a satellite wave. Although the information in a document, an audio sound, and a video image are each quite different in the conventional information transmission, by digitizing broadcast data, they can be transmitted without being separated.
For example, in case of digital data, by transmitting various system information such as EPG (Electric Program Guide) or the like together with video information and audio information, services to the user (viewer) can be improved (the EPG incorporates a function for a recording reservation or the like to a VTR in addition to presenting information such as broadcast schedule, program names, and the like of broadcast programs).
Data in a digital format has a high affinity with information equipment such as a general computer system other than a television. For example, a tuner card for a satellite broadcast is attached to the general computer system, received EPG data is analyzed in the computer, a program table is displayed as a window on a computer display, and a program switching, a recording reservation, or the like can be realized by the operation of a mouse cursor. Naturally, broadcast data can be also digitally recorded as it is onto a hard disk built in the computer.
By transmitting data such as video image, audio sound, and the like other than the broadcast program main body by using a band, interactive performance of the broadcast program can be raised. For example, in case of a broadcast program such that alternative quiz is provided, by transmitting answers together with the video/audio data, on the satellite television broadcast receiver (namely, viewer) side, an answer menu button is prepared on the computer display and marking can be performed in response to the answering operation by a pointing device such as a mouse cursor or the like.
If the interactive performance is further raised, not only a home-use television receiver merely deals with video content but also it can be expected that it jumps as an information control tower. For example, the television receiver can become an Internet terminal or an electronic commerce terminal.
In Japan, the standardizing work regarding digital satellite data broadcast has been being progressed mainly by the ARIB (Association of Radio Industries and Businesses). According to it, in the digital satellite data broadcast, in addition to the audio/video data (AV data) constructing the satellite broadcast program main body, digital transmission data accompanied by the broadcast program is distributed in parallel therewith. More specifically, the program is propagated as a broadcast wave in a format of a “transport stream” (which will be explained below) constructed by multiplexing the AV data compressed by a predetermined compression system such as an MPEG (Motion Picture Experts Group) 2 or the like and the digital transmission data.
An example of broadcast program information which is multiplexed to the digital transmission data is the foregoing EPG (Electric Program Guide: electric program information). The broadcast program information can include particular information regarding the broadcast program main body such as title and date of the broadcast program main body, casting of the program, and the like. The kind of data included in the broadcast program information and its data structure are systematized to a certain extent in accordance with the service content which are provided by the program main body. For example, there are information regarding a menu and ingredients in a cooking program, a vote situation which is successively updated in an election spot news program, a personal record regarding the batting or pitching of each player and a place of a team in a professional baseball relay, and the like.
On the digital satellite data broadcast receiving system (hereinafter, simply referred to as “receiving system”) side, the broadcast program information is displayed by using a partial area of a display screen for displaying and outputting the broadcast program main body. The receiving system is usually constructed by a receiver (set-top-box: STB) for receiving, station selecting, and decoding the broadcast wave and a television for displaying and outputting it and installed to an ordinary home.
A structure of content (hereinafter, referred to as “distribution content”) which is distributed as digital transmission data will now be described with reference to FIG. 13.
As shown in FIG. 13, the distribution content is constructed by: various kinds of monomedia data such as still image, motion image, audio sound, and the like in addition to text data; and a display/output control program (hereinafter, also referred to as a “multimedia encoding application”) which integratedly deals with those monomedia data, that is, as multimedia and specifies a state of the broadcast program information. Reference (link) information for each monomedia data can be built in the display/output control program.
In the foregoing standardizing work of the digital satellite data broadcast by the ARIB, the use of an MHEG (Multimedia and Hypermedia Expert Group) has initially been examined as a format of describing the multimedia encoding application as distribution content. The MHEG is a kind of description language which defines data attributes and presumes an application such that multimedia content is displayed on the television and the viewer extracts desired information in a video-on-demand (VOD) or digital television broadcast. Like a Japanese CS digital broadcast (SKYPerfecTV), there is also a case where the MHEG-5 has already been used.
However, according to the MHEG, an encoding space is fixed and it lacks expandability. That is, since it has to be described by using only the encoding space which has unconditionally been fixed, for example, even if one function (API (Application Programming Interface) or the like) is changed, a considerable correcting work is needed. According to the MHEG, a general recognition degree is low, the data content described by the MHEG is not so frequently circulated, and an affinity with a general computer is relatively low in terms of this meaning.
In the ARIB (mentioned before), therefore, the standardizing work of a data broadcast based on an XML (eXtended Markup Language) is being examined in place of the MHEG.
According to the XML, since a tag is arbitrarily defined, that is, there is no limitation in a method of describing attributes, points that a degree of freedom is high, an affinity with a general computer or Internet is high, and the like can be mentioned as points which are more advantageous than those of the MHEG. A work to set the XML to a description language of the Internet of the next generation is also being progressed.
In case of using the XML as a standard language of the digital satellite broadcast, information of the data for digital broadcast can be exchanged among various kinds of information equipment such as computer, television, telephone, and the like. According to the XML, since the attributes of the tag can be arbitrarily defined, it is stronger against the data processes as compared with the HTML specified to a layout designation. Therefore, the application of the XML to each field including an electronic commerce is also rapidly progressing.
A point that the arbitrary setting of the tag in an XML document means, in other words, that it is an object that a character string written in the document is handled as meaningful data. That is, by the definition of the tag, the tag data divided by each tag can be expressed as data having a meaning other than a mere display object. Further, by defining a structure of the tag, the XML document or the data in the document can be structured and described.
As already mentioned above, in the ARIB, the standardization of the digital satellite data broadcast is being progressed on the basis of the XML. More specifically, the work is separately executed with respect to “basic XML” and “advanced XML” as an expanded edition of the basic XML. According to the basic XML, it is specified that a presentation format which expresses an XML instance onto the display is described by using a tag.
On the other hand, the advanced XML enables attribute information of the XML instance to be added. A rule defining a describing method of the attribute information (that is, grammar of the tag) is a regulation called DTD (Document Type Definition). In the basic XML, the attribute information which is defined by the tag is fixed and the DTD is unnecessary. On the other hand, in the advanced XML, the DTD can be arbitrarily defined. For example, the DTD can be unconditionally defined every field. The attribute information of the tag which is used here includes information that is necessary in the case where when different types of apparatuses such as television receiver and computer are connected, each apparatus mutually understands the meaning of the content and processes the content and the like.
There is also a case where the XML instance itself does not incorporate style information regarding an expressing format. In this case, an expressing method of the XML instance is described by “style sheet” as a document file different from the DTD.
The style sheet is a document file for converting, for example, the XML instance into a format to display and output it onto the display screen (or converting into a print output format to a printer). The style sheet for the XML instance can be described by using, particularly, a language in an “XSL (eXtensible Stylesheet Language)” format, a “CSS (Cascade Stylesheet)” format, or an “XSLT (XSL Transformation)” format as a derivative standard thereof. In dependence on the description of the style sheet, the same DTD content can be expressed by exactly another format by changing font or its size and color and the like. The style sheet is transmitted as a file different from the DTD.
Besides the style sheet, with respect to the multimedia content comprising each monomedia such as audio sound, still image, motion image, and the like, in the XML instance or style sheet, the operation can be also specified by a language called a script different from the XML or XSL. Although such a script is described by a script language such as JavaScript, ECMAScript, Jscript, or the like, according to the standard of the XML, XSL, or the like, fundamentally, it is specified that the script is described by ECMAScript (“ECMAScript” is a script language standardized by European Computer Manufactures Association (ECMA)).
The distribution content comprising the XML document is accompanied with, for example, the DTD document and style sheet besides the XML document. However, there is also a case where the DTD document is not included in the XML document or the style sheet is sent at a timing different from that of the distribution of the XML document. The description language of the distribution content is not always limited to the XML but can also use another markup language format such as SGML (Standard Generalized Markup Language), HTML, or the like. For example, if the XML document is applied to the TV broadcast and operates together with another real-time type data and presentation is performed, there is also a case where monomedia position information in a broadcast data module called URI (Uniform Resource Identifier) of various monomedia content is also built in the XML document main body.
On the receiving system side, the received XML instance is parsing processed by a syntax analyzing program called “XML Parser”. That is, the XML parser analyzes structures of the DTD document and XML instance and outputs a document object. The document object is a structured document whose tree structure has been formed in accordance with the tags in the original XML document. According to the display function of the receiving system, by interpreting the structure of the document, a layout or the like on the screen is determined and can be display outputted to the display.
In case of distributing digital data by transmitting means such as broadcast, network communication, or the like, there is a method whereby the data content such as XML document, script, or the like is data compressed from the original text format to a description of a binary (binary display) format and transmitted.
However, since a file structure of the binary format differs depending on a computer system or software, it can become an obstacle of exchange of the content between an application and a terminal. As an upstream line of the digital satellite data broadcast, the Internet which is connected on the basis of a TCP/IP (Transmission Control Protocol/Internet Protocol) is presumed. According to this Internet, there are historical circumstances such that by using a content distribution in a text format, an environment which does not depend on the kind of terminal and the software has been established.
In the digital satellite data broadcast, therefore, a method of distributing the data content as they are in the text format has been examined in consideration of the affinity with the Internet and the compatibility of the content between platforms.
A size of text data as distribution content becomes a problem here. This is because a load of a transmission path increases and a transmitting efficiency decreases in proportion to the data size.
For example, with the progress of the realization of a high function or the realization of an advanced additional value of the XML document, a document size of the script which specifies the expressing format and operation increases. In future, it is presumed that the data size of script will be larger than that of the XML document main body as a display target itself. An influence which is exerted on a load of a finite band by the distribution of the increased script is large.
Also in a receiving apparatus for receiving the distribution content, it is necessary to prepare a buffer memory of a large capacity in order to receive a large amount of data, causing an increase in costs. Since time that is required for loading into the memory also becomes long, the executing efficiency deteriorates.
In case of using a general computer system as a receiving system, usually, since the memory of a large capacity has been installed as a standard memory, the problem on the memory load is relatively small. On the other hand, in case of a dedicated satellite broadcast receiver such as a set-top-box, since a size of standard memory is generally small, the distribution content of a large capacity is fatal.
It is an object of the invention to provide an excellent data distributing technique which can improve transmitting efficiency of a distribution of content comprising text data.
Another object of the invention is to provide an excellent data distributing technique which can improve execution efficiency in a receiving apparatus for receiving distribution content comprising text data and reduce a memory load.